Digital interfaces of the HDMI standard are widely used as those for transmission of video/audio, etc. The HDMI standard is arranged for AV (Audio Visual) devices by adding an audio transmission function and a copyright protection function to the DVI (Digital Visual Interface) standard which is a digital connection standard between a computer and a display. In the case of the HDMI standard, image (video) data/audio data are transmitted in a mode called TMDS (Transition Minimized Differential Signaling).
The prescription of CEC has been added to the HDMI standards since Version 1.2a (see, e.g., “Supplement 1 Consumer Electronics Control (CEC)” of Nonpatent document 1). This CEC protocol is a control protocol that performs control between devices connected through an HDMI cable. The CEC protocol enables various controls based on unique physical and logical addresses assigned to devices present on an HDMI network. For example, if a user plays back an HDMI-connected DVD (Digital Versatile Disc) player when watching digital broadcasting on a television apparatus, the television apparatus automatically switches input terminal from broadcast receiving terminal to a terminal connected to the DVD player by itself. A menu manipulation displayed by the DVD player, power-on/off, etc., can be performed using a remote controller of the television apparatus.
Terms related to CEC are defined in Nonpatent document 1; those having an HDMI input terminal are defined as sink devices; and those having an HDMI output terminal to output an AV stream are defined as source devices. Those defined as repeater devices have the HDMI input terminal and output terminal to input/output an AV stream and behave as both the sink device and the source device. The sink devices mainly include displaying devices; examples of the source devices include STB (Set Top Box), various players for DVD, BD (Blu-ray Disc), etc., and various recorders for DVD, BD, etc.,; and examples of the repeaters include an AV amplifier, etc.
The HDMI devices are configured to transmit AV streams and associated data associated with the AV streams via one HDMI cable (see, e.g., Patent Document 1). The associated data includes, for example, a CEC message used for inter-device control and an authentication message used for HDCP (High-bandwidth Digital Content Protection) authentication and is mutually exchanged between devices in parallel with the transmission. of AV streams.